1. Field of the Invention
This invention relates to displays, and more particularly to a plasma display panel that is adaptive for improving brightness as well as reducing power consumption.
2. Background of the Related Art
One type of a plasma display panel (PDP) manufactured in large-dimensions is a flat panel display device. A PDP usually controls a discharge period of each pixel in accordance with digital video data to thereby display a picture.
FIG. 1 shows a related-art three-electrode structure that is driven with an AC voltage. In this structure, each discharge cell is arranged in a matrix and includes an upper plate provided with a sustain electrode pair 14 and 16, an upper dielectric layer 18, and a protective film 20 that are sequentially formed on an upper substrate 10. An address electrode 22, a lower dielectric layer 24, barrier ribs 26 and a phosphorous material layer 28 are sequentially formed on a lower substrate 12. The upper and the lower substrates are spaced in parallel by barrier ribs 24.
Each sustain electrode pair 14 and 16 is comprised of transparent electrodes 14A and 16A having a relatively large width made from a transparent electrode material (e.g., ITO) to transmit a visible light, and metal electrodes 14B and 16B having a relatively small width to compensate for a resistance component of the transparent electrodes 14A and 16A. In this case, the transparent electrodes 14B and 16B of the sustain electrode pair and are opposed to each other and are spaced by a gap of approximately 60 μm to 80 μm.
Such a sustain electrode pair and consists of a scan electrode and a sustain electrode. The scan electrode 14 is mainly supplied with a scan signal for panel scanning. The sustain signal for a discharge sustaining, whereas the sustain electrode 16 is mainly supplied with a sustain signal. Electric charges are accumulated in the upper and lower dielectric layers 18 and 24. The protective film 20 prevents a damage of the upper dielectric layer 18 caused by the sputtering to thereby prolong a life of the PDP as well as to improve the emission efficiency of secondary electrons.
The protective film 20 is usually made from MgO. The address electrode 22 crosses the sustain electrode pair 14 and 16. The address electrode is supplied with a data signal for selecting discharge cells to be displayed. The barrier ribs 26 are formed in parallel to the address electrode to thereby prevent ultraviolet rays generated by the discharge from leaking into adjacent discharge cells. The phosphorous material layer 28 is coated on the surfaces of the lower dielectric layer 24 and the barrier ribs 26 to generate any one of red, green and blue visible lights. The discharge space is filled with an inactive gas for a gas discharge.
The discharge cell of the related-art PDP selects a discharge cell by an opposite discharge between the address electrode 22 and the scan electrode 14, and thereafter sustains the discharge by the surface discharge between the sustain electrode pair 14 and 16. The phosphorous material 28 is radiated by an ultraviolet ray generated upon sustain discharge to thereby emit a visible light into the exterior of the cell. Accordingly, the PDP having such discharge cells displays a picture. In this case, the PDP controls a discharge sustain period, that is, a sustain discharge frequency of the discharge cell, in accordance with video data to thereby implement a gray scale required for image display.
An AC surface-discharge PDP of this type performs time-divisional driving of one frame, which is divided into a plurality of sub-fields, so as to realize gray levels of a picture. A light-emission having a frequency proportional to a weighting value of a video data is made in each sub-field period to thereby express a gray level. For instance, if it is intended to display a picture of 256 gray levels using a 8-bit video data, one frame display interval (i.e., 1/60 second=about 16.7 msec) at each discharge cell 11 is divided into 8 sub-fields SF1 to SF8. Each of the 8 sub-fields SF1 to SF8 again is divided into a reset period, an address period and a sustain period, and the sustain period is given by a weighting value at a ratio of 1:2:4:8, . . . , :128. The reset period is a period for initializing the discharge cell, the address period is a period for generating a selective address discharge in accordance with a logical value of a video data, and the sustain period is a period for sustaining a discharge at the discharge cell having generated the address discharge. The reset period and the address period are identically assigned in each sub-field interval.
If electrode widths of the scan electrode 14 and the sustain electrode 16 are narrowly defined in order to reduce power consumption, then a discharge path upon discharge is shortened to thereby limit an light-emission area. Thus, an emission amount of an ultraviolet ray is reduced and hence brightness is deteriorated. On the other hand, if electrode widths of the scan electrode 14 and the sustain electrode 16 are widely defined in order to increase the brightness of the PDP, then a capacitance value becomes large to thereby increase a discharge current and power consumption.
The related-art PDP has a larger screen than other flat panel displays (FPD) such as 40 inch, 50 inch and 60 inch. Such a large screen forces a voltage drop caused by a length of the electrode to have a relatively large difference between the center portion of the discharge cell and the peripheral portion thereof. Also, since a discharge gas at the interior of the PDP is injected at a lower pressure than atmospheric pressure, a force applied to the center portion of the discharge cell where the upper and lower substrates 10 and 12 are supported only by the barrier ribs 26 is different from a force applied to the peripheral portion of the discharge cell, where the upper and lower substrates 10 and 12 are joined to each other by a sealant (not shown). As a result, the PDP of the related-art has a non-discharge area A as shown in FIG. 2, which differ with the size of the panel.
In this related-art PDP, since a length W1 between opposing faces q-ribs 26, which are located between transparent electrodes 14A and 16A to define a gap of a discharge cell as shown in FIG. 3, becomes large, a black brightness rises. Since voltages applied to the transparent electrodes 14A and 16A arranged in parallel to each other is relatively low in the reset period of the PDP, a probability that electrons in the discharge space may be accelerated into more than an ionized energy is relatively low and hence a excitation of neutral atoms caused by a collision of electrons is not active. Thus, the black brightness affects a contrast ratio due to an emission of a slight light generated in the course of transiting neutral atoms from an exciting state into a ground state at a relatively low electron density. Accordingly, the black brightness has to be reduced if it is intended to enhance contrast ratio.
Furthermore, since gaps between the opposite transparent electrodes 14A and 16A within the discharge cell are equal, a discharge is generated between adjacent discharge cells to thereby cause a cross talk.
In order to reduce power consumption, black brightness, and cross talk, another related-art PDP as shown in FIG. 4 is comprised of a sustain electrode pair 64 and 66 that includes transparent electrodes 64A and 66A provided with a stripe part and a head part. The stripe part has a relatively large width and is made from a transparent material (e.g., ITO) to transmit a visible light. The head part expands from the stripe part into the center of the discharge cell. Metal electrodes 64B and 66B having a relatively small width are provided at the stripe part to compensate for a high resistance component of the stripe part. Barrier ribs 76 divide adjacent discharge cells.
The stripe part of each transparent electrode 64A and 66A is formed in a direction crossing the barrier ribs, and the head part thereof expands from the stripe part into the center of the discharge cell such that it does not overlap with the barrier ribs. Thus, each transparent electrode 64A and 66A is expanded such that a transparent electrode material (i.e., ITO) at the non-discharge area overlapping with the barrier ribs 76 is removed, thereby reducing an amount of a current wasted at the sustain electrode pair 64 and 66. Further, since a transparent electrode material (i.e., ITO) at a portion overlapping with the barrier ribs 76 is removed, the transparent electrodes 64A and 66A take part in a discharge independently for each discharge cell.
In this other related-art PDP, a length of the opposite face between the transparent electrodes 64A and 66A within the discharge cell is reduced, because the head part of each transparent electrode 64A and 66A allows each discharge cell to take such a shape that a portion of each transparent electrode overlapping with the barrier ribs 76 is removed. Accordingly, this other related-art PDP can reduce black brightness to thereby enhance contrast ratio.
However, this other PDP raises a phenomenon that a connection of the transparent electrode materials (i.e., ITO) is broken due to an alien substance C or an air bubble D, as shown in FIG. 5, upon patterning of the transparent electrode material in the fabrication process. This is because the transparent electrodes 64A and 66A are connected to the respective metal electrodes 64B and 66B. Therefore, as a result, a discharge current is not applied to the broken transparent material which results in a non-discharge, thereby causing cell binding as indicated by the black. The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.